In systems where an aqueous solution contacts a metallic surface there is always the problem of corrosion of the metal. This is particularly true in heat exchange systems, such as automotive coolant systems. In these systems the aqueous coolant usually contains dissolved calcium ions, may be highly aerated due to a low level of the circulating coolant, and is heated by the heat of combustion of the engine. These are ideal conditions for the formation of rust, scale, and various corrosion products. The problem is aggravated by the use in automotive coolant systems of a variety of metals of fabrication, including cast iron, steel, aluminum, copper, brass, and lead/alloy solders. To a large extent, the corrosion problem can be controlled by the inclusion of various corrosion inhibitors in the coolant or antifreeze composition used in the cooling system. However, particularly when the consumer does not use adequate antifreeze, or renew the antifreeze an regular intervals, scale and corrosion products may accumulate on the metallic surfaces in the cooling system to an extent to seriously impair the cooling efficiency of the cooling system. To clean out these accumulated scale and corrosion products, there have been proposed various cleaners that dissolve the scale and corrosion products. By "scale" is meant any hard, thin coating that adheres to metal surfaces. Scale may be any combination of iron oxides from corrosion, hard water precipitates such as calcium phosphates, or other metal corrosion products.
In order to remove accumulated deposits, cleaner compositions have been proposed containing various acids, reactive salts, and/or chelating agents. For example, Flaxman in U.S. Pat. No. 2,802,733, issued Aug. 13, 1967, discloses a cleaning composition comprising EDTA, sodium tripolyphosphate, sodium acid sulfite, and a mixed mono- and di-oleic acid ester of polyoxethylene glycol. Levy in U.S. Pat. No. 3,419,501 issued Dec. 31, 1968, discloses a cleaning composition comprising an aminopolycarboxylic acid salt, such as tetrasodium EDTA, a nitrate salt, and an alkali metal silicate. Wohlberg in U.S. Pat. No. 3,492,238 discloses a cleaning composition consisting of citric acid, sodium phosphate, sodium hydroxyethylglycine, and sufficient water to maintain the pH between 6 and 7.
Although the prior art compositions, as typified by those described in the above United States Patents, are effective in removing rust and scale, they are not effective in removing solder bloom. Solder bloom is a corrosion product of high lead solders (lead content greater than about 95 wt.%), that remains in situ as it forms. The volume of the solder bloom is much larger than the original solder. As a result, the accumulation of solder bloom around the soldered joints and entrances to the cooling tubes causes a significant decrease in the cross-sectional area and a corresponding decrease in cooling efficiency of the cooling system. Formerly automobile cooling systems were fabricated with solders having a lower lead content, typically about 80 weight percent. With these solders the accumulation of solder bloom is either negligible or non-existent. Starting about 1965, certain automobile manufacturers began using solder with a higher lead content (greater than about 95 wt. % lead). Therefore, as the number of older cars with high-lead solder in their cooling systems has progressively increased, the problem of solder bloom accumulation exists today in millions of cars. Thus, there is an increasing need in the industry for a metal cleaner composition that not only removes scale, and rust, but also removes solder bloom. The applicant is unaware of prior-art cleaner compositions that satisfy this need of removing solder bloom.
An object of this invention is to provide a composition that is effective in the removal of solder bloom from metal cooling systems.
It is also an object of the invention to provide a composition that removes solder bloom, as well as rust, scale and other corrosion products from metal cooling systems.